When an a-Si TFT (Thin-Film Transistor) is exposed to visible light, it may generate a great photocurrent. In a TFT-LCD (Thin-Film Transistor Liquid Crystal Display), for guaranteeing a relatively low leakage current, the channel of the a-Si TFT needs to be shaded from light as much as possible. For instance, there is metal on the backlight side to block backlight and a black matrix on a colour-film glass substrate on the other side to block ambient light. In fact, the leakage current of the a-Si TFT changes accordingly under different light intensities. The brighter the light is, the larger the leakage current will become. Such current is called photocurrent.
With the characteristics of the a-Si TFT photocurrent, it is possible to achieve the photoelectric conversion and optical input, and further to implement an integrated optical touch screen on the TFT-LCD so as to realize integrated touch display manufacturing.
The photoelectric sensor of the prior art optical touch screen, as shown in FIG. 1, consists of a photoelectric TFT T1 for converting an optical signal into an electric signal, a readout TFT T3 for reading the electrical signal to an external circuit for further processing, and a capacitor C1 for maintaining the stability of the electrical signal. In practical application, the drain of the readout TFT T3 is connected to a read line that is usually connected to other readout TFTs. When the electric signal of the current photoelectric sensor is read out, other readout TFTs, even without being turned on, will also generate some leakage currents, which will give rise to noise and render it impossible to detect correctly whether a corresponding position has been touched or not.